You need to select "Publisher's Layout" in Marvin...see the instructions I left in your post in the Marvin forum.
After doing that, Marvin still allows you to change margins, font-size, etc.
Also, the others are referring to the fact that your html file is not "linked" to the css file...in Sigil simply right click (or multi-select) on the file(s) you want to link in the Book Browser section (usually on the left of the window) and select "Link Stylesheets". Without a linked stylesheet all of those class="..." tags won't reference any of the styling.
It will end up looking something like this:
Code:
<head>
<title>Cover</title>
<link href="../Styles/styles.css" type="text/css" rel="stylesheet"/>
</head>